In 1987, the writer began work in shoe factories, he earned many experience in this time. From year of 2001, he teaches in the college, and he start study the shoe technology systematically. The result of study has summarized below.
First thesis: Technical drawing of shoe design
The writer applies standards of mechanical drawing for design of shell pattern.
This solution takes the drawing to useful for cutting rooms as well as for upper closing department / Illustration 1. /
Outer Lining Reinforcement Symbols
Main parts (golosh)
Second thesis: Selection of the method of forme making
Compared with the garment design, the shoe designers are working to smaller tolerance of measurement, a tolerance of pattern is ~ ± 0.5 of mm; of upper is ~ ± 1.0 of mm and of the shoes is ~ ± 2.0 mm. In these conditions, the designer select the work depending on last forme for better result. However, the last has a convex-concave surface, which could not be flattening perfectly. For synonymous result, the writer analyzes the each parts of last’s surface and determine that, after the flattening of the forme shortage of surface is coming. He develops a following process for solve this problem.
- The area-shortage of concave surface must be accept, it will be retrieved later when we design the upper. The concave is being in the joint area of last.
- The area-shortage, which comes from the convex surface can be annihilate with expanding of the forme, thus edge-cutting of the last’s cover.
The edge-cutting still must be consider, we divide for equal chance to shriveling and
area growing, that created from the edge-cutting.
- Briefly, to make the forme we must decide two things, namely the material of the forme and method of flattening of the last’s area.
The writer determine that material of forme /cover/ must be inelastic, the measurements of material no changes after it has picked from the last.
The material can be paper, plastic PVC foil, glue-fabric or adhesive tape. The elastic
materials/ leather/ give different results when we
cover that on the last, we need many experience to use it.
At the flattening of the last’s area, the writer
determines that the best selection is the Middle flat Illustration 2. The researched flats
Symbols Explain of symbols
The first capital letter Show layers of upper: S: outer ; L: lining;
R: reinforcement The second number
Show changing of edge of upper parts before cutting: 0:
unchanged; Plus number: increasing;
Minus number: decreasing.
The third regular letter
Show type of edge of upper parts: r: row edge; f: folding edge; o: underlay edge; c: edge of closed seam; t:
because in this position we can allow the cover to shrivel as equal as expanding. To get this flat we must made one cut / about 10-15mm/ in cover at place of the toe and of the heel / at the convex place/ . / Illustration 2 /
If we flatten out the cover to the Close flat, the girth of the forme not changes / don’t cut anywhere/, then the convex and concave area are maximums, and the area-shortage is also largest, we must retrieve it from somewhere./ Illustration 3a./
If we flatten out the cover to the Open flat, the girth of the forme will grow at the place of cutting /through cut/, and the convex disappears / Illustration 3b/, because of the through cut, the excess of area rise, we must correct some thing on it.
The above solutions are extremists, those are difficult to apply at school, the writer choice a neutral proposal that we flatten out the cover to the middle flat. To this flattening, we cut the cover on half only. The cover can expand and shrivel at once.
The area-shortage remains, but it will be retrieved from a stretch of leather during process of upper lasting. Therefore, the pattern no needs to correct. / Illustration 3c/
The cutting and flattening of cover although determines, the forme making need appropriate practice because materials are different.
a) b) c)
Illustration 3. A flattening of the forme
a) A flattening to a close flat; b)A flattening to an open flat; c) A flattening to a middle flat Table 1.The ratio of shriveling and expanding of last’s cover after flattening
Shriveling of area %
The table 1 shows that the flattening to middle flat reduces the area-shortage much, but it made a few increasing of area. Summary we have advantage, because changes of the area are minimums.
Third thesis: Application of the thickness of material into upper design
Majority of designer handle well in forme making, but many of them do not pay enough attention to use the thickness of material for design.
The thickness of material could take consequence for the fitting of upper to the last, especially in training shoe, which has sponge tongue and sponge collar. Some time, instead of increase the material thickness to the pattern, designer increase a lasting allowance, as result, all of the upper slip to back, and they must correct all of piece of the pattern.
The writer always pays attention to a thickness of material in design when he holds connecting with the last’s measurements. The thickness contains the self- material thickness of the part and the thickness of under covered layers of it.
a) Handling on design of heel curve by material-thickness
The heel curve concerns with length of upper, a material-shortage of it causes deformation of toe and collar of the upper, the handling is follows:
In the normal upper, the heel curve follows the sharp of the back of the forme, and the F point is 3mm inside of forme. This handling regains a lost curve of the forme during flattening. If the collar has sponge, the F point is addition by the sponge thickness outside along of forme / Illustration 4. a, b /
In the upper of training shoe, the sponge is thicker than the normal uppers, and lining has sponge too. In this case, the heel curve must be place outside along the forme by thickness of the sponge. The F point is outside of the forme by about 10-15 of mm, the A point is by 2-3 of mm yet. / Illustration 4.c/
a) b) c)
Illustration 4 .Design the heel curve, a) normal upper; b) normal sponge upper; c) training upper
b) Handling on design of cone by material-thickness
In the training shoe, the tongue is thick, because it has sponge. To design the parts of cone, in first, determine the thickness of tongue and add this worth to forme to get increased area, and then design a eyelet stay and a tongue according to that / Illustration 5/
In designing of tongue, cone area of lining must be reduce by thickness of the tongue, the reducing is compare to the outer, because around of the tongue has a closed seam /Illustration 6/
Illustration 5. The forme of training shoe Illustration 6. Design of tongue
c) Handling on design of bar /strap/ by material-thickness A special feature of bar that, it has
not stiffener which hold it from shrinking after delasting. To design the bar we increase it with thickness of material.
The increasable worth is equal to self-material of the bar and material of under covered parts of it.
At a design of sandal, the length of bar increases with thickness of the outer and lining. In case of shoe design, besides the self-materials of the bar, we
need increase the bar yet with the thickness a)
of materials of eyelet stay and tongue. / Illustration 7/
c) b)
Illustration 7 .a) Design of sandal bar; b), c) Design of shoe bar
Fourth thesis: Determination of a ball line (joint line)
The last always shows the dimensions of our foot. In practice, 10 mm are added to the too end of the last, this addition is so-called safe for the heel-to-toe rocking motion of foot movement.
In surface of the last, anatomy of the foot is not often recognized, this weak point could make trouble for designers, same time a shoes become unusable, because a designer determine wrongly the anatomy of the foot. Many technical literatures in different countries endeavored to find a way to reestablish the anatomy of foot on the last, further on to determine the ball line. In this region, the Hungarian textbook give a best developing, that provides the technicians with valuable method for their designing work.
However, the existing procedures including of ways on graphic and experience are still missing in fashion last which has a long toe. The long toe last give a longer forme, but its anatomy remains. In the longer toe last, the formula to seek the ball line of the normal forme is not applied. The writer introduces a new way to seek the ball line that based on formula of Professor J. P. Zibin and that avoid a toe changing of the last. The formula is follows: / Illustration 8 /
Illustration 8. Determination of the ball line
Draw the forme into a system of XOY coordinates, in the way that the A point laying in Y line and the OA distance equal to heel height of last /hh /. The X line crosses between the two bottom lines of the forme. Measure AB line /raised line/ with followed formula
AB (mm) = Nõ . A + W . B + C
Where: Nõ: Number of the length (point and size) W: Number of width
A, B, C: Coefficients, can be seen in the table
The table of coefficient
Grading systems A B C
EUR 4 0.5 8-16
UK I 5 0.5 71-79
UK II 5 0.5 136-144
CM 6 0.5 8-16
For example:
The length of last is 36 point and the width of last is 6 AB36/6 = 36 . 4 + 6 . 0.5 + 8 = 155 mm
From AB line draw up a ball angle ABD = 980 + heel height /hh /, this line cuts the cone at D point. The BD line will be the ball line that shows a widest place of the last.
According the formula, change of the size of last made also a change in the raised line. So the change of raised line depend from the A coefficient.
For example: AB37/6 = 37 . 4 + 6. 0.5 + 8 = 159 mm Thus: AB37/6 = AB36/6 + A = 155 + 4 = 159mm
The B co-efficient give a change in raised line, if the last changed in the width For example: AB36/7 = 36 . 4 + 7. 0.5 + 8 = 155.5 mm
Thus AB36/7 = AB36/6 + B = 155 + 0.5 = 155.5mm / Illustration 9 /
Illustration 9 Effect of coefficient to the raised line
Fifth thesis: A determination of the long parameter in grading
The shoes are always produced in series, so that the technicians must have a good practice on grading of upper pattern. In Vietnam, the grading remain a hidden and difficult thing among designers, they solve this task with groping or photocopying.
As a result, graded patterns are came into deforming and not satisfy a customs’
requires. The series of shoe product could be organized in 20 sizes, the grading of upper pattern with photocopying is impossible.
The grading is difficult as a consequense of the grading of all kind of the last. The coefficient of grading however changes, it depends
on toe sharp of the last. /Illustration 10./.
The illustration shows that the length of upper is not measured on the length of last, but on a girth of insole. It measured with A, B, C measurements, the two
preceding ones are fixed and the latter a)
one is changes. In the a) case the C measurement
is bigest and in the c) case it could not be seen.
Illustration 10.
Reviewing of the upper measurements
The reviewing show that b)
the C measurement changes according to the sharp of toe last. The finding of it’s change could be difficult determined by formula.
To determine the long parameter of grading, writer develops a new way directly
by the last. First, prepare two c)
piece of a last. A high difference of their sizes is better to earn accuracy measurements.
Then, we make formes from those lasts in similar process. Finally, measure a difference of length of two formes /CH/. We get the parameter of grading for the length. /Illustration 11/.
Illustration 11. Measuring a difference between formes
For example, the length of forme of the H42 = 295 mm, and of the H46 = 322 mm. The relative grading parameter of length is.
β =
Some times, there is only one last for the grading, in the case the other one must be made first.
The parameter of grading for the width can measured directly on the last, in this girth, the measurement of the upper is equal to the last’s.
For example, the girth of ball of B42 = 240 mm, and of the size 46 will be B46 =
Where: Bn = a wanted width, Bo= a start width.
Sixth thesis: Economic analysis of operate of the shoe design equipments a) A period of shoe design process
Many steps of shoe design are artistically, so that the complete mechanization of shoe design could not be economical. Shoe companies organize their technical process on a way on combine of manual and mechanical works considering a size of production.
Table 2. A period of shoe design process
The table 2.estimate a necessary work time of each shoe style. With condition, a cost of manual of working hours are 1.5 US$; a cost of using hours of machinery is 3.9 US$; a price of 2D computer and software is 26,800 US$; 3D computer and software is 70,800 US$ and amortization is 10 years, the sum of cost of design process is
E: Cost of manual work
R: Cost of overhead (35% of the E) G: Cost of amortization of machinery 1. In case of design the new pattern by hand K = (7.67 x 1.5) + 4.03 = 15.53 US$;
2. In case of design the developed pattern by hand K = (4.65 x 1.5) + 2.44 = 9.42 US$;
3. In case of design the new pattern by machine
K = (3.01 x 1.5) + 1.58 + (3.01 x 3.9) =17.83 US$;
4. In case of design the developed pattern by machine K = (0.83 x 1.5) + 0.44 + (0.83 x 3.9) = 4.92 US$.
b) A proposal to build shoe design process considering an economical operation of machinery
According to the above calculations, each case of the manual work and of the mechanical work shows their advantages. For develop an economical shoe design process, the cases could have selectively combined.
Table 3. The optimum design process
Minute 90 43 5 45
Hour 1.5 0.72 0.083 0.75
Sum
133 minutes / 2.22 hours 50 minutes / 0.83 hours The combined process is not necessary to apply the 3D machines, therefore the cost of amortization of machinery has been reduced to 1,07 US$. The sum of cost is below
* In case of design the new pattern
K= (1.5 x 1.5) + (0.72 x 1.5) + 1.17 + (0.72 x 1.07) = 5.27 US$;
* In case of design the developed pattern
K= (0.083 x 1.5) + (0.75 x 1.5) + 0.44 + (0.75 x 1.07) = 2.49 US$.
The successfully prepared technology reduces the sum cost by 33.39% in the new pattern design and it earn a half of sum cost of reducing in the developed pattern design. In spite of the calculation, some shoe manufacturing enterprises could not assemble the optimum design process, because understanding of machinery’ technical features are difficult to apply for their production.
In Vietnam, the mechanization of shoe design for manufactures is not easy arranged, because machine offers of foreign producer are as disorderly as jungle.
Beside of mechanization of shoe design, the manual shoe design is important trained for technician. Like that, they are faster to grasp the machines’ functions.
According to the optimum shoe design process, following formula show scale
* The mechanization’s scale of the new pattern design ,
* The mechanization’s scale of the developed pattern design ,